WOx Interlayer Engineering for Reliable Polarization in HfZrO2 Ferroelectric Capacitors

초록

Post-metallization annealing, even at a low temperature of 350 C-degrees, is essential to induce ferroelectricity in HfZrO2 (HZO) capacitors (FeCAPs). However, this process can also generate an unwanted oxide layer at the non-inert electrode interface. Our findings reveal that a thin substoichiometric WOx is formed on top of a W bottom electrode (BE) owing to the scavenging of oxygen ions from HZO. Oxygen vacancies (V(O)s) generated near the HZO/BE interface cause dipole rotation, rendering the FeCAPs vulnerable to temperature and endurance cycling. We introduce a sputter-deposited amorphous WOx interlayer (IL) at the BE interface and examine the impact on ferroelectric polarization. In the HZO/WO2.4 FeCAPs, many V(O)s in the IL can be clustered during endurance, causing breakdown at 10(4) cycles. However, when a nearly stoichiometric WO3 IL is used, the polarization with increased coercive voltage (V-c) is observed only at a low frequency. This indicates that most of the voltage drop occurs across the insulating WO3 IL rather than across HZO, showing weak remnant polarization (P-r). The optimized WO2.8 IL suppresses V(O)s generation, serving as charge trapping sites near the BE interface and promoting the formation of an orthorhombic phase in HZO, enhancing P-r to 29 mu C/cm(2) over 10(8) cycles. Additionally, unlike the HZO FeCAPs, in which the ferroelectric properties deteriorate at cryogenic temperatures, a P-r greater than 20 mu C/cm(2) at 123 K can be achieved using HZO/WO2.8 FeCAPs.

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